1. Field of the Invention
This invention relates to integrated circuit fabrication, and in particular, dual damascene processing of conductive lines and vias.
2. Background
An integrated circuit is formed by successive fabrication steps of depositing insulative material, forming grooves in the insulative material according to a specific pattern, and filling those grooves with conductive material. The filled material forms conductive lines and vias. Successive layers of conductive material form the integrated circuit elements and their interconnections. This fabrication process is known as damascene processing.
Dual damascene is a process whereby multilevel grooves are formed creating both conductive line openings and via openings to be filled in one process step with conductive material. An insulative material is coated with a resist layer, also known as a photomask, which is exposed to a mask with an image pattern of via openings. The upper half of the insulative material is etched. The photomask is then removed. The insulative material is again coated with a resist layer, which is exposed to a second mask with an image pattern of conductive lines. The insulative material is etched again. Grooves for the conductive lines are formed in the upper half of the insulative material and the already existing via openings are simultaneously etched in the lower half of the insulative material. The grooves are then filled with a conductive material, forming vias and conductive lines.
Dual damascene processing allows simultaneous filling of conductive lines and vias eliminating process steps. However, when using dual damascene processing with soft materials as the insulative material, such as a polymer material, the edges of the via openings are poorly defined due to the dual etchings.